The present invention relates to an electric actuator and a motor used in the actuator, and especially to an electric actuator used in a power tailgate and a power sliding door of an automobile.
It is required for such an electric actuator to be small and light with increased output power since space and weight of the car body are limited.
As shown in JP2005-30545A, an electric actuator comprises a motor casing of a motor part and a gear casing of an actuator part which can be separated from each other. A worm of a shaft in the motor part is engaged with a worm wheel of the actuator part.
A rotor fixed to the base end of the shaft faces a permanent magnet as stator bonded on the inner circumferential surface of the motor casing.
However, when the motor casing is connected to the gear casing in the electric actuator, both are made of Al alloy to make press-fit difficult. So it is necessary to provide a slight clearance between them, which is likely to cause vibration in the motor casing.
Errors in accuracy of the motor casing with respect to the gear casing promotes unevenness in accuracy of the connection of them, making it impossible to keep the clearance between the permanent magnet and rotor constant. Such misalignment makes motor performance decreased.
To improve connection accuracy between the gear casing and motor casing, it is necessary to increase accuracy in working of each casing significantly, which causes not only high cost but also decrease in productivity.
Meanwhile, to fix the permanent magnet as stator on the inner circumferential surface of the motor casing, the magnet is put into the motor casing and heated with drying while adhesive is applied on the outer circumferential surface of the permanent magnet. The three steps make assembling time prolonged.
A working room becomes likely to be contaminated with the adhesive. Also, odor peculiar to the adhesive makes the environment worse, which requires sufficient air conditioning. The edges for the adhesive are likely to cause a gap between the motor casing and permanent magnet or between the permanent magnet and rotor. So balance in motion of the rotor gets poorer.
Furthermore, concentricity of the internal diameter of the permanent magnet to the center is poor after the connection of the motor casing, making it impossible to reduce the gap between the permanent magnet and rotor. Magnetic force of the permanent magnet is not able to efficiently act, which is obstacle against the improvement in motor performance.